问题描述
我在R中有一个数据框，如下所示：
I have a data frame in R that looks like this:
> TimeOffset, Source, Length
> 0 1 1500
> 0.1 1 1000
> 0.2 1 50
> 0.4 2 25
> 0.6 2 3
> 1.1 1 1500
> 1.4 1 18
> 1.6 2 2500
> 1.9 2 18
> 2.1 1 37
> ...
，我想将其转换为
> TimeOffset, Source, Length
> 0.2 1 2550
> 0.6 2 28
> 1.4 1 1518
> 1.9 2 2518
> ...
尝试将其设置为英文，我想将连续记录与同一个源在一起，然后打印出每组中的单个记录，显示该组中的最高时间偏移量，来源和该组中长度的总和。
Trying to put this into English, I want to group consecutive records with the same 'Source' together, then printing out a single record per group showing the highest time offset in that group, the source, and the sum of the lengths in that group.
TimeOffset值得一直增加。
The TimeOffset values will always increase.
我怀疑这是可能的，但我真的不知道从哪里开始。在某种意义上，我可以输出数据帧，并在例如Python，但如果可能，我宁愿留在R中。
I suspect this is possible in R, but I really don't know where to start. In a pinch I could export the data frame out and do it in e.g. Python, but I'd prefer to stay within R if possible.
提前感谢您可以提供的任何帮助
Thanks in advance for any assistance you can provide
推荐答案
首先，您需要创建一个 id 变量，它指定您的组，而不依赖于它们是连续的事实。之后，它很简单。
First you need to create an id variable that specifies your groups without relying on the fact that they are consecutive. After that it is pretty straight forward.
> dat <- data.frame( TimeOffset = c(0,.1,.2,.4,.6,1.1,1.4,1.6,1.9,2.1),
+ Source=c(1,1,1,2,2,1,1,2,2,1),
+ Length=c(1500,1000,50,25,3,1500,18,2500,18,37))
> dat
TimeOffset Source Length
1 0.0 1 1500
2 0.1 1 1000
3 0.2 1 50
4 0.4 2 25
5 0.6 2 3
6 1.1 1 1500
7 1.4 1 18
8 1.6 2 2500
9 1.9 2 18
10 2.1 1 37
>
> id <- cumsum(c(TRUE,diff(dat$Source)!=0))
> id
[1] 1 1 1 2 2 3 3 4 4 5
>
> cbind(TimeOffset=tapply(dat$TimeOffset,id,max),
+ Source=tapply(dat$Source,id,max),
+ Length=tapply(dat$Length,id,sum))
TimeOffset Source Length
1 0.2 1 2550
2 0.6 2 28
3 1.4 1 1518
4 1.9 2 2518
5 2.1 1 37
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